Patients with obstructive sleep apnea (OSA) suffer from repetitive collapse of the airway, resulting in apnea, hypercarbia, and hypoxia, resulting in increased respiratory drive and arousal, with BEG activation and a surge in sympathetic activity and tone in the airway dilator muscles. This cycle re-establishes airway patency, but also causes sleep fragmentation and cardiovascular disease. Despite the critical nature of these events, the brain circuitry that underlies respiratory, EEG, and autonomic arousals during OSA remains unknown. In this PPG, we hypothesize that the parabrachial nucleus (PB) plays a key role in arousals in OSA, as a nodal point in receiving sensory input during apnea, and activating arousal responses. Projects 1 and 5 will examine the circuitry underlying EEG and autonomic (Project 1) and respiratory (Project 5) arousals directly, by tracing the inputs and outputs from PB neurons that respond to hypercarbia. These projects will also use a conditional knockout strategy to test whether the PB neurons that cause arousal use glutamate as their main neurotransmitter. Project 4 will test the role of the PB neurons in arousal, and examine their relationship with the basal forebrain neurons that play a major role in relaying the PB arousal influence to the cerebral cortex. It will test antidromic and orthodromic activation of PB and basal forebrain neurons recorded across wake-sleep states in unrestrained rats, and determine how their firing rate changes during both hypercarbic and auditory arousals. Project 3 will focus on the role of the orexin neurons in the lateral hypothalamus in relaying the arousal influence from the PB. By using mice with conditional knockouts for the orexin type 1 and 2 receptors, the role of the different orexin receptors at specific forebrain targets in producing arousal will be tested. Project 2 is a translational study that tests whether some patients with OSA have a high threshold for arousal, permitting greater hypoxia during airway collapse. It will test whether this threshold is altered by CPAP treatment and whether a novel treatment with a non-myorelaxant hypnotic drug can stabilize breathing in a subset of OSA patients with lower arousal thresholds. This work will help to design interventions for improving the health of patients with OSA.